<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>淡入淡出</title>
<style>
    #div1{width: 200px;height: 200px;background: green;filter:alpha(opacity=0.3);opacity:0.3;}
</style>
<script type="text/javascript">
    window.onload=function(){
        var oDiv=document.getElementById('div1');
        oDiv.onmouseover=function(){//鼠标移入
            startMove(100);
        };
        oDiv.onmouseout=function(){//鼠标移出
            startMove(30);
        };
    };
    var alpha=30;
    var timer=null;
    function startMove(iTarget){
        var oDiv=document.getElementById('div1');
        clearInterval(timer);
        timer=setInterval(function(){
            var speed=0;
            if(alpha<iTarget){
                speed=5;
            }else{
                speed=-5;
            }
            
            if(alpha==iTarget){
                clearInterval(timer);
            }else{
                alpha+=speed;
                oDiv.style.filter='alpha(opacity='+alpha+')';
                oDiv.style.opacity=alpha/100;
            }
        },30);
    }
</script>    

</head>
<body>
    <div id="div1">
    </div>
</body>
</html>